This invention relates generally to gas turbine engines, and more specifically to ducts which carry high temperature fluids within gas turbine engines.
At least some known gas turbine engines include a core engine having, in serial flow arrangement, a fan assembly and a high pressure compressor which compress airflow entering the engine, a combustor ignites a fuel-air mixture which is then channeled through a turbine nozzle assembly towards low and high pressure turbines which each include a plurality of rotor blades that extract rotational energy from airflow exiting the combustor. Furthermore, at least some known gas turbine engines include ducting that routes high temperature fluids from one area of the engine for use in another area of the engine. For example, ducting may carry high temperature bleed air having a temperature of at least 1000xc2x0 F. for use in an engine anti-icing system.
As the high temperature fluids flow through the ducting, an external surface of the ducting may rise in temperature through heat transfer. However, such ducting may be routed through areas of the engine which are not as thermally resistant as the ducting. For example, in at least some known gas turbine engines, to facilitate minimizing the possibility of igniting flammable fluids, such as but not limited to hydraulic fluid, an external surface temperature limit of less than 400xc2x0 F. is imposed on the external surfaces of the anti-icing ducting.
To facilitate reducing an external touch temperature of the ducting, at least some known ducting is wrapped with insulation. Furthermore, to maintain the structural rigidity and integrity of the ducting, the ducting is coupled to the engine with metallic bracket assemblies. To facilitate providing structural support to the ducting, without facilitating heat transfer through the support, at least some known bracket assemblies include inner tube supports that extend circumferentially around the duct.
Each inner tube supports has a substantially frusto-conical or wish-boned cross-sectional profile defined by a radially outer portion and a radially inner portion which are connected together at an apex that is substantially parallel the duct external surface. Insulation is then wrapped around the duct in the area between the inner tube supports, and a separate outer tube support is then welded or otherwise joined to the inner tube supports and the duct. Alternatively, the outer tube support is coupled to the supports and insulation material is injected into the cavity. To facilitate a reduction in the external surface touch temperature at locations along the tube and a distance from the supports, insulation is wrapped around the duct adjacent to each inner tube support, prior to a polyimide outer wrap, or a wrap fabricated from a similar composite based material, being extended around the insulation and a portion of the outer tube support. A mounting bracket is then coupled to the outer tube support. In another alternative embodiment, the outer tube support incorporates the mounting bracket, in the form of a casting.
However, during operation, stress concentrations may develop at the apex formed at the connection between the radially outer and radially inner portions of the inner tube supports. This stress is primarily caused by temperaturre induced axial and radial growth differences between the outer tube support and the pressure ducting. Over time, cyclic operation of the engine with such stress concentrations may lessen the useful life of the bracket assembly and/or the duct. Furthermore, because of the multiple components that must be assembled and aligned during assembly of such ducts, manufacturing such bracket assemblies and assembling such ducts may be time-consuming and costly process.
In one aspect, a method for coupling a duct to a gas turbine engine casing is provided. The method comprises extending a first inner tube support member circumferentially around the duct, such that a radially inner side of the first inner tube support is against the duct, and wherein the first inner tube support member has a substantially curved cross sectional profile extending between the radially inner side of the first inner tube support, and a radially outer side of the first inner tube support. The method also comprises extending an outer tube support member circumferentially around the first inner tube support member such that the outer tube support member is against the first inner tube support member outer surface, and coupling the outer tube support member to the gas turbine engine casing.
In another aspect of the invention, a bracket assembly for a duct is provided. The bracket assembly includes a first inner tube support member that extends circumferentially around the duct, and an outer tube support member that extends circumferentially around the first inner tube support member. The first inner tube support includes a radially outer side, a radially inner side against the duct, and a body extending therebetween, wherein the body has a substantially smooth arcuate cross-sectional profile extending between the radially inner and outer sides.
In a further aspect of the invention, a duct for a gas turbine engine including a casing is provided. The duct includes a tube for transporting a fluid therein, and a bracket assembly for securing the tube to the engine casing. The bracket assembly is configured to reduce heat transfer from the tube to the engine casing. The bracket assembly includes a first inner tube support member and an outer tube support member. The first inner tube support member extends circumferentially around the tube such that a radially inner side of the first inner tube support member is against the tube. The outer tube support member extends circumferentially around the inner tube support member, such that a radially outer side of the first support member is against the outer tube support member. The first inner tube support member has a substantially semi-elliptical cross-sectional profile extending between the first inner tube support radially inner and outer sides.